The present invention relates generally to thermal treatment systems, and more particularly to a method and apparatus for controlling thermal dosing in a thermal treatment system.
Thermal energy, such as generated by high intensity focused ultrasonic waves (acoustic waves with a frequency greater than about 20 kilohertz), may be used to therapeutically treat internal tissue regions within a patient. For example, ultrasonic waves may be used to ablate tumors, thereby obviating the need for invasive surgery. For this purpose, piezoelectric transducers driven by electric signals to produce ultrasonic energy have been suggested that may be placed external to the patient but in close proximity to the tissue to be ablated. The transducer is geometrically shaped and positioned such that the ultrasonic energy is focused at a xe2x80x9cfocal zonexe2x80x9d corresponding to a target tissue region within the patient, heating the target tissue region until the tissue is coagulated. The transducer may be sequentially focused and activated at a number of focal zones in close proximity to one another. This series of xe2x80x9csonicationsxe2x80x9d is used to cause coagulation necrosis of an entire tissue structure, such as a tumor, of a desired size and shape.
In such focused ultrasound systems, the transducer is preferably geometrically shaped and positioned so that the ultrasonic energy is focused at a xe2x80x9cfocal zonexe2x80x9d corresponding to the target tissue region, heating the region until the tissue is necrosed. The transducer may be sequentially focused and activated at a number of focal zones in close proximity to one another. For example, this series of xe2x80x9csonicationsxe2x80x9d may be used to cause coagulation necrosis of an entire tissue structure, such as a tumor, of a desired size and shape.
By way of illustration, FIG. 1A depicts a phased array transducer 10 having a xe2x80x9cspherical capxe2x80x9d shape. The transducer 10 includes a plurality of concentric rings 12 disposed on a curved surface having a radius of curvature defining a portion of a sphere. The concentric rings 12 generally have equal surface areas and may also be divided circumferentially 14 into a plurality of curved transducer sectors, or elements 16, creating a xe2x80x9ctilingxe2x80x9d of the face of the transducer 10. The transducer elements 16 are constructed of a piezoelectric material such that, upon being driven with a sinus wave near the resonant frequency of the piezoelectric material, the elements 16 vibrate according to the phase and amplitude of the exciting sinus wave, thereby creating the desired ultrasonic wave energy.
As illustrated in FIG. 1B, the phase shift and amplitude of the respective sinus xe2x80x9cdrive signalxe2x80x9d for each transducer element 16 is individually controlled so as to sum the emitted ultrasonic wave energy 18 at a focal zone 20 having a desired mode of focused planar and volumetric pattern. This is accomplished by coordinating the signal phase of the respective transducer elements 16 in such a manner that they constructively interfere at specific locations, and destructively cancel at other locations. For example, if each of the elements 16 are driven with drive signals that are in phase with one another, (known as xe2x80x9cmode 0xe2x80x9d), the emitted ultrasonic wave energy 18 are focused at a relatively narrow focal zone. Alternatively, the elements 16 may be driven with respective drive signals that are in a predetermined shifted-phase relationship with one another (referred to in U.S. Pat. No. 4,865,042 to Umemura et al. as xe2x80x9cmode nxe2x80x9d). This results in a focal zone that includes a plurality of 2n zones disposed about an annulus, i.e., generally defining an annular shape, creating a wider focus that causes necrosis of a larger tissue region within a focal plane intersecting the focal zone. Multiple shapes of the focal spot can be created by controlling the relative phases and amplitudes of the emmitted energy from the array, including steering and scanning of the beam, enabling electronic control of the focused beam to cover and treat multiple of spots in the defined zone of a defined tumor inside the body.
More advanced techniques for obtaining specific focal distances and shapes are disclosed in U.S. patent application Ser. No. 09/626,176, filed Jul. 27, 2000, entitled xe2x80x9cSystems and Methods for Controlling Distribution of Acoustic Energy Around a Focal Point Using a Focused Ultrasound System;xe2x80x9d U.S. patent application Ser. No. 09/556,095, filed Apr. 21, 2000, entitled xe2x80x9cSystems and Methods for Reducing Secondary Hot Spots in a Phased Array Focused Ultrasound System;xe2x80x9d and U.S. patent application Ser. No. 09/557,078, filed Apr. 21, 2000, entitled xe2x80x9cSystems and Methods for Creating Longer Necrosed Volumes Using a Phased Array Focused Ultrasound System.xe2x80x9d The foregoing (commonly assigned) patent applications, along with U.S. Pat. No. 4,865,042, are all hereby incorporated by reference for all they teach and disclose.
It is significant to implementing these focal positioning and shaping techniques to provide a transducer control system that allows the phase of each transducer element to be independently controlled. To provide for precise positioning and dynamic movement and reshaping of the focal zone, it is desirable to be able to alter the phase and/or amplitude of the individual elements relatively fast, e.g., in the xcexc second range, to allow switching between focal points or modes of operation. As taught in the above-incorporated U.S. patent application Ser. No. 09/556,095, it is also desirable to be able to rapidly change the drive signal frequency of one or more elements.
Further, in a MRI-guided focused ultrasound system, it is desirable to be able to drive the ultrasound transducer array without creating electrical harmonics, noise, or fields that interfere with the ultra-sensitive receiver signals that create the images. A system for individually controlling and dynamically changing the phase and amplitude of each transducer element drive signal in phased array focused ultrasound transducer in a manner which does not interfere with the imaging system is taught in commonly assigned U.S. patent application Ser. No. [not-yet-assigned; Lyon and Lyon Attorney Docket No. 254/189, entitled xe2x80x9cSystems and Methods for Controlling a Phased Array Focussed Ultrasound System,xe2x80x9d], which was filed on the same date herewith and which is hereby incorporated by reference for all it teaches and discloses.
Notably, after the delivery of a thermal dose, e.g., ultrasound sonication, a cooling period is required to avoid harmful and painful heat build up in healthy tissue adjacent a target tissue structure. This cooling period may be significantly longer than the thermal dosing period. Since a large number of sonications may be required in order to fully ablate the target tissue site, the overall time required can be significant. If the procedure is MRI-guided, this means that the patient must remain motionless in a MRI machine for a significant period of time, which can be very stressful. At the same time, it may be critical that the entire target tissue structure be ablated (such as, e.g., in the case of a malignant cancer tumor), and that the procedure not take any short cuts just in the name of patient comfort.
Accordingly, it would be desirable to provide systems and methods for treating a tissue region using thermal energy, such as focused ultrasound energy, wherein the thermal dosing is applied in a more efficient and effective manner.
In accordance with a first aspect of the invention, a thermal treatment system is provided, the system including a heat applying element for generating a thermal dose used to ablate a target mass in a patient, a controller for controlling thermal dose properties of the heat applying element, an imager for providing preliminary images of the target mass and thermal images during the treatment, and a planner for automatically constructing a treatment plan, comprising a series of treatment sites that are each represented by a set of thermal dose properties. By way of non-limiting example only, the heat applying element may apply any of ultrasound energy, laser light energy, radio frequency (RF) energy, microwave energy, or electrical energy.
In a preferred embodiment, the planner automatically constructs the treatment plan based on input information including one or more of a volume of the target mass, a distance from a skin surface of the patient to the target mass, a set of default thermal dose prediction properties, a set of user specified thermal dose prediction properties, physical properties of the heat applying elements, and images provided by the imager. The default thermal dose prediction properties are preferably based on a type of clinical application and include at least one of thermal dose threshold, thermal dose prediction algorithm, maximum allowed energy for each thermal dose, thermal dose duration for each treatment site, cooling time between thermal doses, and electrical properties for the heat applying element. The user specified thermal dose prediction properties preferably include at least one or more of overrides for any default thermal dose prediction properties, treatment site grid density; and thermal dose prediction properties not specified as default thermal dose prediction properties from the group comprised of thermal dose threshold, thermal dose prediction algorithm, maximum allowed energy for each thermal dose, thermal dose duration for each treatment site cooling time between thermal doses, and electrical properties for the heat applying element.
Preferably, the treatment plan ensures that the entire target mass is covered by a series of thermal doses so as to obtain a composite thermal dose sufficient to ablate the entire target mass, and the thermal dose properties are automatically optimized using physiological properties as the optimization criterion. Preferably, the planner limits the thermal dose at each treatment site in order to prevent evaporation or carbonization.
In a preferred embodiment, the planner constructs a predicted thermal dose distribution in three dimensions, illustrating the predicted thermal dose threshold contours of each treatment site in the treatment plan. A User Interface (UI) may also be provided for entering user specified thermal dose prediction properties and for editing the treatment plan once the treatment plan is constructed. A feedback imager for providing thermal images may also be provided, wherein the thermal images illustrate the actual thermal dose distribution resulting at each treatment site. In one embodiment, the imager acts as the feedback imager.
In accordance with another aspect of the invention, a focused ultrasound system is provided, including a transducer for generating ultrasound energy that results in thermal doses used to ablate a target mass in a patient, a controller for controlling thermal dose properties of the transducer, an imager for providing preliminary images of the target, and for providing thermal images illustrating an actual thermal dose distribution in the patient, and a planner for automatically constructing a treatment plan using the preliminary images, the treatment plan comprising a series of treatment sites represented by a set of thermal dose properties used by the controller to control the transducer.
The planner preferably constructs a predicted thermal dose distribution illustrating the predicted thermal dose contours of each treatment site in the treatment plan, wherein after a thermal dose is delivered to a treatment site in the treatment plan, the actual thermal dose distribution is compared to the predicted thermal dose distribution to determine remaining untreated locations within the target mass. The planner preferably automatically evaluates the treatment plan based on the remaining untreated locations and will update the treatment plan to ensure complete ablation of the target mass is achieved by adding treatment sites, removing treatment sites, modifying existing treatment sites, or leaving the treatment plan unchanged. In some embodiments, a user can manually adjust the treatment plan based on the remaining untreated locations.
Preferably, the imager provides outlines of sensitive regions within the patient where ultrasonic waves are not allowed to pass, wherein the processor uses the outlines in constructing the treatment plan so as to avoid exposing the sensitive regions to ultrasound.
In accordance with still another aspect of the invention, a method of controlling thermal dosing in a thermal treatment system is provided, which includes selecting an appropriate clinical application protocol, the selected application protocol having associated with it certain default thermal dosing properties; retrieving relevant magnetic resonant images for thermal dose planning; tracing a target mass on the images; entering user specified thermal dosing properties and selectively modifying the default thermal dosing properties; and automatically constructing a treatment plan representing thermal doses to be applied to treatment sites, the treatment plan based on the default thermal dosing properties and the user specified thermal dosing properties.
In preferred implementations, tracing the target mass can be done manually or automatically, and may include evaluating the target mass to ensure that obstacles including bones, gas, or other sensitive tissue will not interfere with the thermal doses and repositioning a patient or a heat applying element in order to bypass any such obstacles. Preferably, the treatment plan ensures that a target mass receives a composite thermal dose sufficient to ablate the target mass, wherein automatically constructing the treatment plan includes predicting and displaying a predicted thermal dose distribution. Preferably, automatically constructing the treatment plan further includes calculating limits for each thermal dose to be applied to each treatment site in order to prevent evaporation or carbonation.
In a preferred implementation, the treatment plan may be manually edited, including at least one of adding treatment sites, deleting treatment sites, changing the location of treatment sites, changing thermal dosing properties, and reconstructing the entire treatment plan with new thermal dosing properties.
In one implementation, the method includes applying a low energy thermal dose at a predetermined spot within the target mass in order to verify proper registration, and evaluating said predetermined spot and adjusting and/or re-verifying if necessary. In a following step, the low energy thermal dose could be extended to a full dose sonication that will be evaluated to assess the thermal dosing parameters as a scaling factor for the full treatment.
Other aspects and features of the invention will become apparent hereinafter.